1. Field of the Invention
The present invention relates to a liquid crystal shutter, more particularly to a liquid crystal shutter using an optically compensated bend (OCB) mode.
2. Description of the Background Art
The liquid crystal technology widely put in practical use by a display is also applied to various kinds of shutters, such as a window capable of adjusting transmissivity and a pair of glasses capable of controlling transmissivity and light blocking effect, by electric signals.
The liquid crystal is used for the shutter having high-speed response characteristics, which shows parallax images for right and left eyes by time sharing, respectively in a three dimensional display system. Recently, the shutter has been used in commercial base for the fields, such as amusement, education, broadcast, and medical treatment.
For example, Japanese Patent Application Laid-Open No. P 1996-327961 discloses the three dimensional display system using the liquid crystal shutter glasses, which has regions for right and left eyes. Although a twisted nematic (TN) type liquid crystal, a super twisted nematic (STN) type liquid crystal, and a ferroelectric liquid crystal are introduced to make the liquid crystal shutter, the liquid crystal of the TN type or the STN type has insufficient response speed. Moreover, although the ferroelectric liquid crystal has superior characteristics such as high speed response, the ferroelectric liquid crystal requires an improvement in reliability, such as shocking-proof and temperature characteristics.
On the other hand, an OCB (Optically Compensated Bend) liquid crystal using π cell is proposed. In the OCB mode, since a bend alignment of the liquid crystal is used, a high-speed response suitable for a liquid crystal shutter is obtained. Furthermore, there is also no problem of reliability, such as shocking-proof and temperature characteristics because the nematic liquid crystal is used.
In the OCB mode, at the time of power supply ON, the liquid crystal is transferred once to the bend alignment from an original splay alignment. After the liquid crystal is operated, the liquid crystal returns from the bend alignment state to the splay alignment state at the time of power supply OFF. If the transition of the alignment of the liquid crystal is made unevenly, the region where the alignment is different from other regions may be visible as spot-like unevenness. Accordingly, the quality of the liquid crystal shutter deteriorates. Since external force such as an electric signal is not applied at the time of power supply OFF, it is difficult to control the transition of the alignment.